Specifications

PENTIUM® PRO PROCESSOR AT 150, 166, 180, and 200 MHz E
42
V
REF
V
REF
+ 0.2
V
REF
- 0.2
Time
V
start
δ
φ
τ
3
.0
V
/
n
s
0
.3
V
/
n
s
ρ
α
10 ps rise/fall Edges
1.5 V Clk Ref
Clock
T
su
+0.05ns
Figure 25. Standard Input Hi-to-Lo Waveform for Characterizing Receiver Ringback Tolerance
ρ and δ are respectively, the amplitude and duration
of square-wave ringback, below the threshold voltage
(V
REF
), that the receiver can tolerate without
increasing T
SU
by more than 0.05 ns for a given pair
of (α, τ) values.
If, for any reason, the receiver cannot tolerate any
ringback across the reference threshold (V
REF
), then
ρ
would be a negative number, and δ may be infinite.
Otherwise, expect an inverse (or near-inverse)
relationship between ρ and δ, where the more the
ringback, the shorter is the time that the ringback is
allowed to last without causing the receiver to detect
it.
φ is the final minimum settling voltage, relative to the
reference threshold (V
REF
), that the input should
return to after ringback to guarantee a valid logic
state at the internal flip-flop input.
φ is a function of the input amplifier gain, its
differential mode offset, and its intrinsic maximum
level of differential noise.
Specifying the values of α, τ, ρ, δ, and φ is the
responsibility of the receiver vendor. The system
designer should guarantee that all signals arriving at
such a receiver remain in the permissible region
specified by the vendor parameters as they
correspond to those of the idealized square waves of
Figure 24 and Figure 25. For instance, a signal with
ringback inside the box delineated by ρ and δ can
have a τ equal to or longer than the minimum, and an
α equal to or larger than the minimum also.
A receiver that does not tolerate any ringback would
show the following values for the above parameters:
α ≥ 0V, τ ≥ T
su
, ρ = −200 mV, δ = undefined, φ =
200 mV.
A receiver which tolerates 50 mV of ringback would
show the following values for the above parameters:
α ≥ 0V, τ = data sheet, ρ = −150 mV, δ = data sheet,
φ ≥ tens of mV (data sheet).
Finally, a receiver which tolerates ringback across
the switching threshold would show the following
values for the above parameters:
α ≥ 0 V, τ = data sheet, ρ ≥ 0 mV (data sheet), δ =
data sheet, φ ≥ tens of mV.
where δ would usually be a brief amount of time,
yielding a pulse (or “blip”) beyond V
REF
.